1. Field of the Invention
The invention relates to methods and apparatus for segmenting a page of image data into windows and for classifying the image data within each window as a particular type of image data.
2. Related Art
Image data is often stored in the form-of multiple scanlines, each scanline comprising multiple pixels. When processing this type of image data, it is helpful to know the type of image represented by the data. For instance, the image data could represent graphics, text, a halftone, condone, or some other recognized image type. A page of image data could be all one type, or some combination of image types.
It is known in the art to take a page of image data and to separate the image data into windows of similar image types. For instance, a page of image data may include a halftone picture with accompanying text describing the picture. In order to efficiently process the image data, it is known to separate the page of image data into two windows, a first window representing the halftone image, and a second window representing the text. Processing of the page of image data can then be efficiently carried out by tailoring the processing to the type of image data being processed.
It is also known to separate a page of image data into windows and to classify and process the image data within the windows by making either one or two passes through the page of image data. The one pass method is quicker, but it does not allow the use of "future" context to correct information that has already been generated. In a two pass method, information obtained for a third or fourth scanline can be used to generate or correct information on a first or second scanline. In other words, future context can be used.
In a two pass method, during the first pass, the image is separated into windows, and a judgment is made about the type of image data in each window. At the end of the first pass, the image type for each pixel is recorded in memory. During the second pass, the information from the first pass, i.e., the image type data, is used to process the image data. Unfortunately, storing image type information for each pixel of a page of image data requires a great deal of memory, which increases the cost of an apparatus for performing this method.